1. Field of the Invention
The present invention relates to a process for preparing a low stress agent coated with rubber and an epoxy composition containing the low stress agent. When used in semiconductor encapsulants, the low stress agent absorbs inner and outer stresses in a molded article of organic composite materials and exhibits higher reliability.
2. Description of the Prior Art
For preparing the compounds for use in semiconductor encapsulants, a mixture of organic materials such as epoxy resins and inorganic fillers has been used to produce a molding compound having desired properties such as electric insulation and moldability at a reasonable level.
However, as semiconductor devices are integrated in a very large-scale, as the sizes of semiconductor chips become larger and smaller and as the size of memory cells becomes smaller, it is required in the art to modify such compounds so that they have improved characteristics.
In the prior art, an inorganic filler treated with a coupling agent has been used in compounds as shown in Japanese Patent Publications Nos. 61-78823 and 61-136548. This method made the cured article i.e., the molded article made by encapsulating a semiconductor device with the compound, highly water resistant, but an increase in modulus of the cured article caused by the coupling agent led to an increase in inner stress, which causes a problem in that the ratio of crack occurrence on the layer of the semiconductor devices becomes higher due to thermal shock.
These are known methods such as blending or reacting rubber in compounds as shown in Japanese Patent Publications Nos. 61-62514, 61-133225 and 61-148227 to improve the physical properties of organic materials in the compounds, i.e., epoxy resin or phenol resin. However, there are many problems in the molding process since the rubber bleeds out during molding treatment and as a result of this, may stain the mold. In order to prevent the above mentioned bleeding out, there are other types of methods, such as addition of reactive liquid polymer as shown in Japanese Patent Publications Nos. 61-148227 and 61-26671 or reacting to synthetic rubbers, silica and silane coupling agents as shown in Japanese Patent Laid-Open Publication No. 60-188418. However, the former causes a problem such as lowering of a second glass transition temperature and the hardness of the curing article, while the latter fails to decrease the modulus.